Standard audio connectors or plugs are available in three sizes according to the outside diameter of the plug: a 6.35 mm (¼″) plug, a 3.5 mm (⅛″) miniature plug and a 2.5 mm ( 3/32″) subminiature plug. The plugs include multiple conductive regions that extend along the length of the connectors in distinct portions of the plug such as the tip, sleeve and one or more middle portions between the tip and sleeve resulting in the connectors often being referred to as TRS (tip, ring and sleeve) connectors.
FIGS. 1A and 1B illustrate examples of audio plugs 10 and 20 having three and four conductive portions, respectfully. As shown in FIG. 1A, plug 10 includes a conductive tip 12, a conductive sleeve 14 and a conductive ring 16 electrically isolated from the tip 12 and the sleeve 14 by insulating rings 17 and 18. The three conductive portions 12, 14, 16 are for left and right audio channels and a ground connection. Plug 20, shown in FIG. 1B, includes four conductive portions: a conductive tip 22, a conductive sleeve 24 and two conductive rings 25, 26 and is thus sometimes referred to as a TRRS (tip, ring, ring, sleeve) connector. The four conductive portions are electrically isolated by insulating rings 27, 28 and 29 and are typically used for left and right audio, microphone and ground signals.
When plugs 10 and 20 are 3.5 mm miniature connectors, the outer diameter of conductive sleeve 14, 24 and conductive rings 16, 25, 26 is 3.5 mm and the insertion length of the connector is 14 mm. For 2.5 mm subminiature connectors, the outer diameter of the conductive sleeve is 2.5 mm and the insertion length of the connector is 11 mm long. Such TRS and TRRS connectors are used in many commercially available MP3 players and smart phones as well as other electronic devices. Electronic devices such as MP3 players and smart phones are continuously being designed to be thinner and smaller and/or to include video displays with screens that are pushed out as close to the outer edge of the devices as possible. The diameter and length of current 3.5 mm and even 2.5 mm audio connectors are limiting factors in making such devices smaller and thinner and in allowing the displays to be larger for a given form factor.
Some manufacturers have used USB, mini-USB and micro-USB connectors as audio connectors to connect headphones and similar audio components to electronic devices. FIG. 2 is an example of a micro-USB connector 30, the smallest of the USB connectors. Connector 30 includes an outer housing 32 and a metallic shell 34 that is inserted into a corresponding receptacle connector. Shell 34 defines an interior cavity 38 and includes five contacts 36 formed within the cavity. The insertable shell portion 34 of connector 30 is both thinner and shorter than even the 2.5 mm subminiature version of connectors 10 and 20. Connector 30, however, suffers from other drawbacks that detract from the overall user experience. For example, connector 30 must be inserted into its respective receptacle connector in a particular orientation, yet it is difficult for the user to determine when connector 30 is oriented in the correct insertion position. Also, even when connector 30 is properly aligned, the insertion and extraction of the connector is not precise, has an inconsistent feel and, even when the connector is fully inserted, has an undesirable degree of wobble that may result in either a faulty connection or breakage. Additionally, cavity 38 is prone to collecting and trapping debris within the cavity which may interfere with the signal connections.